Arc suppression circuit



April 1955 TUNG CHANG CHEN ARC SUPPRESSION cmcurr 2 Sheets-Sheet 1 Filed Aug. 4. 1951 FIG.2

mvem'oa TUNG CHANG CHEN ATTORNEY 4 April 5, 1955 TUNG CHANG CHEN ARC SUPPRESSION CIRCUIT Filed Aug. 4, 1951 FIG. 3

2 Sheets-Sheet 2 FIG. 4

INVENTOR TUNG CHANG CHEN BY ATTORNEY United States Patent ARC SUPPRESSION CIRCUIT Tung Chang Chen, Havertown, Pa., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Application August 4, 1951, Serial No. 240,385

3 Claims. (Cl. 317-11) This invention relates generally to are suppression circuits and more particularly to the type are suppression circuit which is especially adaptable for use in connection with the deenergization of relay windings and other inductive circuits.

It has been found that when the winding of a relay is caused to become deenergized it is frequently desirable and sometimes necessary to use some form of arc suppression in order to protect the equipment involved. The majority of the relays of the telephone type, for example, require a winding current in the order of from 60 to 100 milliamperes for normal operation. The induced voltages generated from the interruption of the operating current often will cause visible arcing and damage to the contacts and may be high enough to present the possibility of the coil insulation itself breaking down. In determining desirable arc suppression characteristics the two most important problems involved are the arcing at the contacts which may be quantitively considered by the magnitude of the induced voltage and the effects of the arc suppression circuit on the release time of the relay. The function of an ideal arc suppression circuit would be to cause the stored energy of the relay to dissipate itself in such a manner that the voltage across the coil never becomes larger than the applied voltage. It is preferable that this not be done at the expense of an extremely long release time.

With no arc suppression circuit the normal release time of a relay is generally entirely acceptable for most circuit applications. If the addition of an arc suppression circuit does not increase the release time over this normal value, it may be considered satisfactory. With some types of arc suppression circuits the release time may be reduced considerably below this normal value. Furthermore, in some circuits the release time is not critical in which case only the arcing of the contacts caused by the induced voltage has to be considered.

The basic considerations of arc suppression may be considered by examining what happens when the inductive circuit is opened. The stored energy must dissipate itself through some sort of energy loss, usually 1 R loss, and the function of an arc suppression circuit is to provide a path for this dissipation in order that this energy will not be dissipated as 1 R loss through the arc. It is important to note that when an arc is formed at the contact, the energy available is not only that stored in the coil, but the coil voltage source now has a path to continue its flow of energy until the arc is broken. The voltage that is generated by the coil is of a magnitude determined by and of a polarity opposite to that assumed by the coil when it is energized by the coil voltage source. The induced voltage of the coil will add to that of the source in the series circuit comprising source, contacts, and coil.

The function of an ideal arc suppression circuit is to provide a zero impedance path shunting the coil at the instant of opening the switch connecting the coil voltage source to the coil and when the distance between the contacts of the switch has increased to a point where it will not sustain an are at any voltage (infinite separation of contacts for this ideal case), the inductive coil should be shunted by infinitely high impedance. The zero impedance is to short circuit the induced voltage of the contacts and the infinite resistance at a later time is to dissipate the energy in zero time, theoretically. There are various arc suppression circuits disclosed in the prior art which in varying degrees attempt to meet these conditions. However, in these prior art devices, one of the two desirable characteristics must be sacrified in order to obtain the other. As discussed above, the two desirable characteristics are low induced voltage and short release time.

An object of the present invention is to improve arc suppression circuits generally.

Another object is to provide a novel arc suppression circuit which limits the induced voltage and reduces the deenergization time of the inductive load to minimum values.

Still another object of the invention is to increase the reliability of arc suppression circuits.

Generally speaking, in carrying out this invention there is provided a series arrangement of a battery source and an asymmetrical device connected in parallel with an inductive load such as a relay winding, the asymmetrical device being arranged so that its forward impedance is presented to the positive potential of the voltage induced in the inductive load when deenergized and the battery source being connected so that its polarity is opposed to this induced voltage.

Further in accordance with the invention the battery source may be made common to a large number of relay windings, thus reducing the number of elements required to protect these windings and the contacts controlling energization and deenergization thereof.

These and other objects and features of the invention will be more fully understood from the following detailed description and the drawing in which:

Fig. 1 is a schematic diagram showing an inductive circuit utilizing the invention;

Fig. 2 is a chart showing the real and imaginary operation characteristics of the inductive load of Fig. 1 when used in conjunction with the arc suppression circuit also shown in Fig. 1;

Fig. 3 is a schematic diagram of a system comprising a plurality of inductive loads wherein the voltage source of the arc suppression circuits is common to all of the loads; and

Fig. 4 is a schematic diagram of a circuit having a plurality of inductive loads with a common power supply and further having a system of arc suppression circuits with common power supplies which protect the inductive loads and associated circuit regardless of which terminals of the inductive loads are disconnected from the said common power supply.

Referring now to Fig. 1, 48 volt battery source 10 forms a power supply for an inductive load which may have an inductance of any value. In the illustrative circuit shown in Fig. 1, however, assume that the load consists of an inductance 11 having a value of about .5 henry and a resistance 60 of about 1000 ohms. These values are typical of telephone type relays. Contacts 12 and 13 provide means for electrically connecting and disconnecting power supply 10 to the load.

In order to prevent an are from forming across the contacts when they are opened to disconnect the load from the source 10 there is provided, in accordance with the invention, an arc suppression circuit connected across the inductive load and which comprises a volt battery source 14 and an asymmetrical device 15.

Asymmetrical device 15 in the example being discussed should have a cathode to anode impedance able to withstand a potential difference not less than the sum of the potentials of battery source 10 and battery source 14 without drawing excessive reverse currents. Typical of the type asymmetrical devices which can be used are selenium rectifiers, copper oxide rectifiers, germanium diodes, and other suitable rectifiers. It is to be understood that for different applications, the values and characteristics of gatery source 14 and asymmetrical device 15 will also In Fig. 2 curve 16 represents the typical exponential curve of current decay vs. time if an inductive load such as load 11 of Fig. l were short-circuited simultaneously with the disconnection therefrom of its power supply such as power supply 10. Curve 17 is another typical exponential curve illustrating the transient current caused to flow in inductance 11 if a voltage source such as battery 14 were suddenly applied across the inductive load. This curve is based on the assumption that contacts 12 and 13 are open and that asymmetrical device 15 is not present in the circuit. Curve 18 represents the resultant current caused to flow through the inductive load as a result of the superpositioning of the effects of battery source 10 and battery source 14 represented by curves 16 and 17 respectively. It will be noted that in actual operation the current represented by curve 17 and the current represented by the portion of the curve 18 below the current value is imaginary. However, for purposes of analysis of the operation of the circuit, these imaginary currents are herein considered.

In Fig. 3 one battery supply is utilized in a plurality of inductive circuits. The common battery source is designated in Fig. 3 as element 25 and is common to asymmetrical devices 24, 26, and 27 which, in turn are associated with inductances 22, 28, and 29 respectively. Common battery source 21 comprises the energizing power supply for the inductances 22, 28, and 29. Resistances 23, 32, and 33 represent the resistances of the associated inductances plus any other resistance in series with associated inductances. The values of the circuit constants used in the circuit of Fig. 3 are determined by the same considerations which determine the values of the circuit constants of the circuit of Fig. 1.

In Fig. 4 there is illustrated an application of the invention to a system having a plurality of inductive loads 35, 36, and 37 with a common power supply 38. Each of the inductive loads 35, 36, and 37 may be selectively disconnected from either terminal of the common power supply 38 by means of switching means positioned on either side of each of the inductive loads. For example, inductive load 35 has associated therewith contacts 39 and 40. Opening of contacts 39 will disconnect the inductance 35 from the positive terminal of common power supply 38 and opening of contacts 40 will disconnect the inductance 35 from the negative terminal of the common power supply 38.

The arc suppression circuits are divided into two main groups, each having a common power supply. More specifically, the first of these groups of arc suppression circuits consists of asymmetrical devices 41, 42, and 43 which have a common biasing voltage 44. It will be noted that the negative terminal of the common biasing voltage 44 is connected to the anodes of asymmetrical devices 41, 42, and 43. The second group of asymmetrical devices consists of asymmetrical devices 45, 46, and 47 which have a common biasing voltage 48. The positive terminal of the common biasing voltage 48 is connected to the cathodes of asymmetrical devices 45, 46, and 47. The first group of asymmetrical devices 41, 42, and 43 and the associated biasing voltage perform the function of arc suppression when the contacts 39, 53, and 54 connecting the inductive loads 35, 36, and 37 to the positive terminal of the common power supply 38 are opened. More specifically, if contacts 39 associated with inductive load 35 were opened to interrupt a current through inductance 35, asymmetrical device 41 and biasing voltage 44 would constitute the arc suppression circuit. The second group of asymmetrical devices 45, 46, and 47 and associated biasing voltage 48 protect the inductive circuit from excessive arcing when contacts 40, 48, and/or 49 are opened to disconnect the inductive loads 35, 36, and 37 respectively from the negative terminal of common power supply 38. The resistances 50, 51, and 52 represent the inherent resistance of inductances 35, 36, and 37 respectively and also any additional resistance which might be connected in series with these inductances.

Referring now to Fig. 1 the operation of the circuit shown therein will be described. Assume that contacts 12 and 13 are closed so that battery source is electrically connected across the inductive load comprising inductance 11 and resistance 60 and further assume that a steady condition has been reached wherein a current of 48 milliamperes is flowing through the inductive load as shown at zero time by curve 16 of Fig. 2. No appreciable current will be flowing through asymmetrical device inasmuch as its high back impedance is presented to positive terminal of battery source 10 and its low forward impedance is presented to the negative terminal of battery source 14.

If contacts 12 and 13 are then 85 opened, the energy stored in inductance 11 would, in the absence of asymmetrical device 15 and battery source 14, tend to dissipate itself through opening contacts 12 and 13. However, due to the presence of the circuit comprising asymmetrical device 15 and battery source 14, the energy stored in inductance 11 will dissipate itself through the circuit comprising asymmetrical device 15 and battery source 14. In the absence of battery source 14 dissipation of the energy in inductance 11 will follow curve 16. It will be noted that when contacts 12 and 13 are opened, the inductive load comprising inductance 11 and resistance 60 forms a series circuit with the battery source 14 and the asymmetrical device 15 in which the asymmetrical device 15 is so connected that it presents a very low impedance to the dissipating current fiow of the inductive load.

Battery 14, as has hereinbefore been stated, is connected within the circuit in such a manner that its polarity is opposite to the polarity of the voltage induced in the inductive load when the contacts are opened. By the well known method of circuit analysis known as superposition, the effect of battery source 14 upon the circuit can be considered independently of any other voltages. This effect is shown by curve 17 which represents an imaginary current flow through the inductive load upon the opening of contacts 12 and 13. The two opposed current flows caused by the inductive load and the battery source 14 and represented by curves 16 and 17, respectively, may then be added together to obtain the actual resultant current flow from the circuit following the opening of contacts 12 and 13. This current flow is represented by curve 18. The maximum current which exists at the time of the opening of contacts 12 and 13 is represented at 0 time and is of a value of 48 milliamperes. The current represented by curve 18 of Fig. 2 is shown as decreasing to 0 and then flowing in'the opposite direction which is herein defined as a negative current. This, however, can not actually occur in the circuit due to the asymmetrical device 15 which will not permit a negative current to flow therethrough. Thus, the current is cut ofi at 0 value and the energy in the inductive load is completely dissipated. It is to be observed that the battery source 14 in reality never delivers current to the inductance 11. Consequently. battery source 14 can have a comparatively low power capacity. It will be noted further that the asymmetrical device 15 conducts current only in the direction of its forward impedance and only in its normal operating range. Under no normal circumstances of ordinary operation is the asymmetrical device overloaded. The cathode to anode impedance of the asymmetrical device is never caused to conduct excessive current. Consequently, its life will be much greater than in those arc suppression circuits wherein the asymmetrical devices utilized are caused to conduct excessive reverse currents under normal operating conditions.

Referring now to Fig. 3 the operation of the circuit shown therein will be described. Assume that contacts 19 have been closed and that inductance 22 has a steady current flowing therethrough from battery source 21. Upon the opening of contacts 19 the current flow through inductance 22 will then be caused to seek another path which may be traced from inductance 22, resistance 23, conductor 34, battery source 25, asymmetrical device 24, back to inductance 22. The battery source 25 and asymmetrical device 24 comprise the arc suppression circuit for the inductance 22. Similarly, the energy stored in inductance 28 will be dissipated through battery 25 and asymmetrical device 26 when contacts are opened, and the energy stored in inductance 29 will be dissipated through battery and asymmetrical device 27 when contacts are opened. The curves of Fig. 2 apply to the arc suppression circuits of Fig. 3 as well as to the arc suppression circuit of Fig. 1. It is to be noted that the only distinction between Figs. 1 and 3 is that in Fig. 3 the voltage source 25 which comprises a part ofthe arc suppression circuits and which corresponds to. voltage supply 14 of Fig. l, is common to a plurality of arc suppression circuits, whereas, the battery source 14 of Fig. l is individual to asymmetrical device 15 and inductance 11.

Referring now to Fig. 4 the operation of the circuit illustrated therein will be described. Assume that contacts 39, 40, 53, 54, 48, and 49 are closed, and further assume that a steady state current is flowing through inductive loads 35, 36, and 37 from the common power supply 38. No appreciable current will be flowing from biasing battery source 48 or biasing battery source 44 inasmuch as asymmetrical devices 45, 46, and 47 will effectively block current flow from battery 48 and asymmetrical devices 41, 42, and 43 will block current flow from battery source 44. If contact 39 is suddenly opened, there will remain in inductance 35 a certain amount of energy determined by LI where L is the inductance and I is the current flow therethrough at the time the contacts 39 are opened. Since the current path including battery source 38 and inductance 35 is now broken, the current flowing through inductance 35 at the time contacts 39 are opened must then follow a circuit which may be traced from inductance 35 through resistance 50, contacts 40, conductor 55, battery source 44, asymmetrical device 41 and back to inductance 35. It can be seen that battery source 44 and asymmetrical device 41 comprise the arc suppression circuit for inductance 35 when contacts 39 are opened. In theory, the operation of this arc suppression circuit is the same as has been explained with respect to Fig. 1.

Assume now that contacts 39, 40, 53, 48, 54, and 49 are all closed and that a steady state current has been attained in inductances 35, 36, and 37. Assume that under such conditions contacts 40 are opened. This disconnects the power supply 38 from inductance 35. However, the energy contained in inductance 35 will be dissipated through some circuit. This circuit may be traced from inductance 35 through resistance 50, asymmetrical device 45, biasing battery source 48, conductor 56, contacts 39 and back to inductance 35. In this example, it can be seen that asymmetrical device 45 and biasing battery source 48 comprise the arc suppression circuit for inductance 35. Here again, as in the case of the opening of contacts 39, the theory of operation of the arc suppression circuit is the same as has been discussed with respect to Fig. 1.

In a manner similar to that just described, the asymmetrical device 46 and the common battery source 48 comprise the arc suppression circuit for inductance 36 when contact 48 is open, the asymmetrical device 47 and the common biasing battery source 48 form the arc suppression circuit for inductance 37 when contacts 49 are opened, the asymmetrical device 42 and common biasing battery source 44 form the arc suppression circuit for inductance 36 when contacts 53 are opened, and the asymmetrical device 43 and common biasing battery source 44 form the arc suppression circuit for inductance 37 when contacts 54 are opened. It is to be noted that the circuit constants used if Fig. 4 are determined by the same factors which control the choice of circuit constants of the circuits shown in Fig. 1.

It is to be understood that the circuits described herein are but preferred embodiments of the present invention and that various changes may be made in values of circuit constants, applications, and arrangements without departing from the spirit or scope thereof.

I claim:

1. In an electrical circuit comprising a plurality of inductive impedances, a first battery means for energizing said inductive impedances, said first battery means having a negative terminal and a positive terminal, first contact means to selectively disconnect said inductive impedances from said positive terminal of said first battery means, second contact means to selectively disconnect said inductive impedances from the negative terminal of said first battery means, a first plurality of asymmetrical devices having their cathodes individually and respectively connected to the points between said first contact means and said inductive impedances, a second battery means having its negative terminal connected to the anodes of said first plurality of asymmetrical devices and its pos1t1ve terminal connected to the negative terminal of said first battery means, a second plurality of asymmetrical devices having their anodes individually and respectively connected to the points between said second contact means and said inductive impedances, a third battery means having its positive terminal connected to the cathodes of said secondplurality of asymmetrical devices and its negative terminal connected to the positive terminal of said first battery means.

2. In an electrical circuit comprising at least one inductive load impedance, a source of D. C. energizing power having a positive terminal and a negative terminal and means including switches located at opposite ends of said load impedance for connecting opposite sides of said impedance to respective terminals of said source of D. C. power for energizing and deenergizing said impedance, a first arc suppression circuit electrically connected in parallel with said inductive impedance between one side thereof and one terminal of said D. C. power source, a second arc suppression circuit electrically connected in parallel with said impedance between the other side of said impedance and the other terminal of said D. C. power source, each of said are suppression circuits comprising a substantially constant D. C. voltage source and at least one asymmetrical device, said asymmetrical device being connected between one terminal of said voltage source and one side of said impedance, the other terminal of said voltage source being connected to the other side of said impedance, said voltage source being of such polarity as to oppose the voltages induced in the impedances when deenergized and said asymmetrical device being connected so as to present its low impedance to current flow resulting from such induced voltages.

3. In an electrical circuit comprising a plurality of inductive impedances, a source of D. C. energizing power having a positive and a negative terminal and means including switches located at opposite ends of said impedances for connecting opposite sides of each of said impedances to respective terminals of said source of D. C. power for selectively energizing and deenergizing said impedances, a first arc suppression circuit means electrically connected in parallel with said inductive impedances between one side of each of said impedances and one terminal of said D. C. source, a second arc suppression circuit means electrically connected in par allel with said impedances betwen the other side of each of said impedances and the other terminal of said D. C. source, each of said arm suppression means comprising a substantially constant D. C. voltage source and a plurality of asymmetrical devices, said asymmetrical devices being connected between one terminal of said voltage source and one side of respective ones of said impedances, the other terminal of said voltage source being connected to the other side of said impedances, said voltage source being connected to oppose the voltages induced in the impedances when they are deenergized and said asymmetrical devices being connected so as to present their low impedances to current flow resulting from such induced voltages.

References Cited in the file of this patent UNITED STATES PATENTS 2,637,769 Walker May 5, 1953 FOREIGN PATENTS 3,882 Great Britain Feb. 12, 1914 of 1913 759,031 France Jan. 27, 1934 

